Cathode ray tube controlled relay means



June 151, 1965 MAsAo TAKAG: ETAL 3,189,780

GTHODE RAY TUBE CONTROLLED RELAY MEANS Filed April 1, 1963 2Sheets-Sheet l MASAO TAKAGI ETAL CATHODE RAY TUBE CONTROLLED RELAY MEANSJupe 15, 1965 2 Sheets-Sheet 2 Filed April l, 1963 CIRCUIT 3,189,769CATHDE RAY TUBE CNTRGLLED RELAY MEANS Masao Talragi, lUlyo-iru, Kyoto,and Keizo Yamaii, iviishima-gnn, @salta-Su, lapapa, assignors to TateisiDenki Kabushilriiraisha, Kyoto, Saipan, a corporation of apan Filed Apr.1, i963, Ser. N 269,475 Claims priority, application Japan, Apr. 7, i962(utility models), 37/l7,755, 37/f17,756 7 Ciairns. (Cl. 315-10) Thisinvention relates to relay means and, more particularly, to relay meansin which a cathode-ray tube and photoelectric means are employed to openor close electric circuits when a predetermined value of voltage hasbeen reached.

Meter relays are adapted for general use as means for opening or closinga circuit when voltage under supervision has arrived at a predeterminedlevel. These relays are generally provided with a needle which is ableto be preset to a certain position and another needle which is movablein response to a given signal. Each of the needles carries a contactwhich is to be brought in touch with a contact mounted on the other. Inresponse to a given signal, the movable needle is moved until the signalattains a predetermined level, when the two contacts touch -to produce acontrol signal to `actuate a relay.

Because of their mechanical construction, such meter relays have seriousshortcomings: for example, the mechanical movable needle cannot respondinstantaneously to a given signal due to the relatively great moment ofinertia acting thereupon, especially when the signal liuctuates intotransient values; and the existence of contacts involves many problemssuch as overheating due to contact resistance.

Accordingly, the primary object of this invention is to provide meansfor controlling electric circuits by output control signals producedwhen input signals arrive at predetermined levels, wherein no mechanicalmovable members such as a needle are employed. Instead, the relay meansof the invention employs: a cathode-ray tube so constructed that theelectron beam is deected in accordance with a given electrical signaland strikes a fiuorescent screen at a position thereon corresponding tothe beam detlection so as to cause a luminous area to appear at thatposition; and light-sensitive means for receiving light from ltheluminous area on the screen of the tube when the given signal hasattained a predetermined level, and producing a signal to open or closethe electric circuit under control. Thus, in accordance with theinvention no mechanical movable members such as needles are used, sothat the above defects encountered in the meter relay can be eliminated.

Other objects, features and advantages of the invention will be moreapparent from the following detailed explanation of preferredembodiments of the invention with reference to the accompanyingdrawings, wherein:

FIGURE l is a schematic showing of an embodiment of the invention, withthe cathode-ray tube and photoelectric means having their Walls cut-awayto show the insides thereof;

FlGURE 2 is a side sectional view of the cathode-ray tube andphotoelectric means of FIGURE 1;

FIGURE 3 is a schematic, partially cut-away view of the cathode-ray tubeand photoelectric means of another embodiment of the invention;

FIGURE 4 is a side sectional view of FIGURE 3;

FIGURE 5 is a schematic side view of another embodiment of theinvention;

FlGURE 6 is a schematic bottom plan view of FIG- URE 5;

ld@ Patented ,inne l5, i965 FIGURE 7 is a schematic block diagram ofanother embodiment of the invention;

FIGURE 8 is a schematic diagram ofthe limiter circuit of FIGURE 7;

FIGURE 9 is a schematic block diagram of still another embodiment of theinvention;

FIGURE 10 is a schematic diagram of the Schmitt circuit of FIGURE 9; and

FIGURE 11 is a schematic diagram of the NOT circuit of FIGURE 9.

The invention comprises: a cathode-ray tube including a iluorescentscreen, electron gun means for emitting electrons, forming saidelectrons into a beam and focusing said beam onto said screen in aluminous area, and means for deiiecting said beam; means for applying anelectrical signal to said deilecting means; photoelectric meansincluding a photoelectric element for receiving light from said luminousarea, said photoelectric means being so positioned relative to saidscreen that said photoelectric element receives light from said luminousarea only when said electrical signal has reached a predetermined level;and means for opening or closing electric circuits in response to asignal produced when said photoelectric element is excited by light fromsaid luminous area on said screen.

Referring in detail to FIGURES 1 and 2, there is shown a cathode-raytube l including an electron gun generally designated at Z, a deflectionsystem 3 consisting of a single pair of plates spaced apartsymmetrically about the axis of the gun and having flared ends, and aliuorescent screen 4 deposited on the inside of the end `face of thetube. The tube is shown flat and the screen is of an elongatedrectangular shape. Although the illustrated shapes are preferred, theymay be of any other suitable shape. The electron gun consists of acathode 5, a control grid 5', a first accelerating electrode 5, a secondaccelerating electrode 6, a beam-forming electrode 7 having an apertureformed therein, a focusing system 8 consisting of a pair of spacedplates, and a third accelerating electrode 9.

Electrons emitted from cathode 5 are accelerated as they pass throughaccelerating electrodes S, 6, formed by the aperture of electrode 7 intoa beam having an elongated, narrow rectangular section, focused by meansof focusing system 8, further accelerated by electrode 9, and then passbetween deliecting plates 3. Within the space between the plates thereis created an electrostatic field whose strength is determined by thestrength of an electrical signal applied thereto. The electric signalmay be `derived from any electrical phenomenon to be supervised, or anyquantity to be regulated. For example, in the measurement of voltage,the signal may be derived from the voltage under measurement or avoltage proportional thereto; or if a quantity is to be automaticallycontrolled, the signal may be derived from a voltage corresponding tothe quantity.

To .the deilecting plates are connected terminals 11), l, between whichis impressed `a signal voltage such :as described just above. Thiscreates an electrostatic field proportional in magnitude .to the appliedvoltage. As the elect-ron beam passes through the electrostatic field,it is deflected an amount proportional to the magnitude of the held and,consequently, to the voltage under measurement or the quantity under:automatic control. The beam deflected in this manner finally strikes4the uorescent lscreen at 1a position corresponding to the beamdeliection so as to produce there a defined, luminous area. Preferably,the luminous area .on the screen takes the form lof a line, preferablyextending along the short axis of the screen from the upper to the loweredge thereof. When the `applied voltage changes, the deflection angle ofthe beam also changes, causing the luminous area on the screen to movealong the long axis of the screen a distance corresponding to the beamdeilection.

rThe `structure of the cathode-ray tube of the invention `and itsoperation in connection with the electron beam deflection differ from.those of ordinary cathode-ray tubes, as follows: While ordinarycathode-ray tubes are provided with two sets of deiiecting plates, thatis, horizontal `and Vertical deflection plates, the cathode-ray tube ofthe invention is provided with a single set of deecting plates so thatthe electron beam is deflected in .such a manner that displacement ofthe luminous `area on the screen takes place .along only onepredetermined. axis of the screen. `If desired, there may be providedtwo or more sets of deecting plates of the same function, that is,detlecting their respective beams individually in the :same direction.In ordinary cathode-ray tubes, lthe luminous Iareajon the screen musttake no other form than a tiny spot, whereas in the tube of theinvention it may be a spot or a line or of any other suitable shape.Finally, the cathode-ray tube of the invention is prefer-ably hat,compared with ordinary `funnel-shaped tubes.

IIf a calibrated plate Iis provided for indicating the position of theluminous area on the screen, it will be possible to read the magnitudeof the electrostatic field between the -deliecting plates and,consequent-ly, that of the voltage under measurement or the quantityunder supervision, since any slight change in the Voltage or thequantity results in a corresponding lchange in the 4magnitude of theelectrostatic Ifield and, consequently, in the position of the luminousarea on the screen.

In front of the screen 4 there is placed a photoelectric means generallyindicated 12 at such a position that it may receive light from theluminous area on the screen when the :area has moved to that position onthe screen. The photoelect-ric means comprises a casing 13 with an openend facing the screen of the cathode-ray tube, a convex lens 14 iittedinto the open end `of the casing, and a photoeiect-ric element -15enclosed in the casing. The lens serves to collect light from theluminous .area on the screen and focus it onto the photoelectricelement. The element may be composed of any `photoelectric material.Most widely used in cadmium sulfide which Vis highly sensitive to lightin the visible region of the spectrum, and the most suitable is agermanium phototransistor.

The photoelectric element is connected to the input side of an amplifier16, at the output side of which appears yan ampliiied voltage when thephotoelectric element is ,appropriately illuminated. The loutput voltagecontrols an electric circuit, as through an auxiliary relay y17. Therelay may be of an electromagnetic type having .an energizing coi-l 1S,which is excited by the output of the amplifie-r to open or closecontacts 19, 20,

Mention has .already been made that a change in the voltage applied t-othe deflecting plates causes a corresponding change in the `deiiect-ionangle of the electron beam and, consequently, :a correspondingdisplacement or K the luminous area on the screen of the cathode-raytube. If the displacement is such that light from the luminous areaenters photoelectric means 12 preset to a certain position and excitesphotoe-lectric element 115, the output of amplifier 16 actuates relay17. By selectively varying the position of the photoelectric means alongthe length of the screen, it is possible to regulate the value of thevoltage applied to the deflecting plates when the relay is caused tooperate. In other words, it is possible to detect that the voltage undermeasurement or the quantity under supervision has passed a predeterminedvalue, and to take a proper measure such as eliminating the cause of theevent through operation of relay 17.

With a single photoelectric means, it is possible to de- .rect that thevoltage applied to the deflecting plates and, consequently, the quantitybeing supervised have passed through, that is, either increased frombelow to above or decreased from above to below, a predetermined level.

With .a Vpai-r of photoelectric means spaced a desired distance .apartfrom each other as shown in FIGURE `l or 3, it is possible to place boththe upper and lower limits on the voltage under super-vision and detectthat the voltage has gone out of the range. More than tworphotoelectricmeans may of course be provided, =In this case, the photoelectricelement in each of the plurality of photoelectric means is excited whenthe luminous area moving across the screen has passed a positioncorresponding .to the position of each of the plurality of photoelectricmeans. Therefore, it is possible to detect the voltage under supervisionhaving passed each of a plural-ity of predetermined values.

In accordance with the invention, the voltage to be applied .to thedeiiecting plates of the cathode-ray tube may be either direct oralternating. When it is alternating, one -cycle of the voltage causesone reciprocating Imovement of the luminous area across the screen. Thedistance to be traversed by the 'luminous area varies with the amplituderof the applied voltage. When the amplitude of the voltage and,consequently, that of movement or" the luminous area has exceeded apredetermined vaiue, the photoelectric element in a photoelectric meanscorresponding to the value is excited by the light from the luminousarea to actuate relay 17.

For-the purpose of .the invention, lens 14 is not `always required. Whenthere is only a slight amount of light 4falling on the photoelectricelement, however, the convex lens helps to collect yand focus the lightonto the element.

In the embodiment of FIGURES l and 2, the convex lens 14 is fitted intothe open end of casing 13. In the embodiment of FIGURES 3 and 4,however, the end face of the cathode-ray tube 1, on the inside of whichis deposited a iluorescent screen 4, isV formed into a .convex lens 21extending over the length of the screen. Vlfhe len-s may occupy thewhole end face of t-he tube, or either of .the upper and lower sectionsextending lengthwise of the tube face. The -lens may also occupy themiddle section extending lengthwise of the tube. The function of thelens is quite the same as that of FIGURES l and 2.

As previously mention-ed in connection with explanation of theembodiment of FIGURES 1 and 2, it is preferable that the photoelectricmeans be `so arranged as to be selective-ly movable to any desiredposition along the length of screen 4. FIGURES 5 and 6 shows anotherembodiment of the invention provided with means suitable for suchselective movement of the photoelectric means. To explain in furtherdetail, the end face of the Ifiat cathode-ray tube 1 and, consequently,the screen 4 4is for-med into a `circular arc. A iixed shaft 31 isdisposed either above or below the 4tube and concentric with the cent-erof the .arc of the Screen. ARotatable about the shaft is mounted anL-shaped lever 32 with its bent, free end carrying a photoelectric means12 so that whereever along the arc of the screen the photoelectric meansmay have been rotated about the shaft to be positioned, it always yfacesthe screen equidistantly spaced therefrom. Thus it becomes quite easy tomove the photoelectric means to any desired position along the length4of the screen, and to keep constant the amount of light falling uponthe photoelectric element from the luminous area on the screen,regardless of the relative position of the photoelectric means. When aplurality of phot-oelectric means are provided, they are mounted ontheir respective L-shaped levers in the above-mentioned manner. InFIGURE 6 there are shown two L-shaped levers 32 carrying theirrespective photoelectric means 12.

Mention has already been made that as the voltage applied to the.deflecting plates of t-he cathode-ray tube varies, the luminous area onthe screen moves across it. If the movement is too fast, it oftenhappens that the luminous area runs past a position corresponding to thepreset position of a photoelectric means too rapidly for thephotoelectric element enclosed therein to 4receive a suicient amount oflight to cause relay 17 to be actuated.

aisa'reo 5 FIGURES 7 and 8 show another embodiment of the inventionprovided with circuit means especially directed toward solving thisproblem. The circuit is arrange-d so that when the voltage applied tothe deflecting plates of the cathode-ray tube varies enough to cause theluminous area on the screen to move beyond ythe preset position of thephotoelectric means, the voltage is limited to such a value as to make.the luminous area stay vat the required position so that -t-hephotoelectric element may receive a suiicient amount of light from theluminous area for the relay to be actuated.

To explain the circuit arrangement in further detall with refe-rence toFIGURES 7 and 8, a deiiecting circuit 41 is connected to the deectingplates 3 which are enveloped in a flat cathodearay tube 1 with auorescent screen 4 deposited on the inside of the tube face. To theinput side of the deecting circuit is connected a limiter circuit 42, tothe terminal 43 of which is applied la voltage corresponding to aquantity under supervision. The limiter circuit applies its output tothe deiiecting circuit, which in turn applies to the deflecting platesits output signal voltage proportional to its input, that is, the outputfrom the limiter circuit. It will need hardly mentioned that because ofthe limiter circuit, no voltage higher than a predetermined level willbe applied to lthe deflecting circuit 41.

As shown in FIGURE 8, the limiter circuit 42 has a tube 44 shown as atriode which functions as .a limit tube. This -tube has its anode 45connected to an output terminal 46, to which is to be connected thedeflecting circuit 41. The grid 47 of tube 44 is connected to theterminal 43. In order to vary the output of the limiter circuit, avariable resistor 49 is connected to the grid 47 of .tube 44:-, and theslider 50 of this resistor is connected to the photoelectric means 12 insuch a manner that setting the slider to a point of the resistor resultsin a cor-responding setting of the photoelectric means to a positionalong the length f the screen. 'It will be easily seen that the value ofgrid bias applied to tube le and, consequently, the value of its outputvoltage is determined by the setting of variable resistor 49.

Suppose that the slider 5G is in Contact with a point T of resistor 49.The portion of the resistance existing between the point T and ground Gwill determine the value of grid bias, which will in tu-rn determine thev-alue of voltage appearing at terminal 46. Suppose that this outputvoltage is 80 v. 'Simultaneously with the setting of the slider 50, thephotoelectric means i2 has been moved along the -length of the screen toa position corresponding to lthe position on the screen to which theluminous area on the screen is to be displaced when a voltagecorresponding to the output, now supposed to 4be 80 v., of `the limitercircuit 42 is impressed on the deiiecting plates 3. With thephotoelectric means thus positioned, so Along as the voltage undersupervision is below 8O v., the luminous area on the screen will not bedisplaced enough for light therefrom to -fall on the photoelectricelement in the photoelectric means. lEven if the Voltage happens to riseabove 80 v., the circuit 42 l-imits it and holds it at 8O v., therebypreventing the luminous area on the screen from moving beyond theposition corresponding to 8O v., and keeping the luminous area stayingat that position so that light therefrom falls on the photoelectricelement in an amount great enough for rel-ay 17 to be actuated withoutfail.

With the arrangement of FIGURES 7 and 8, in order for the photoelectricelement to receive enough light from the luminous area on the screen ofthe cathode-ray tube for reliable operation of relay 17, the voltage tobe applied to the deflecting plates is regulated so as to prevent theluminous area from moving beyond a position corresponding to the presetposition of the photoelectric means. To accomplish the same purpose, thecircuit arrangement of FGURES 9, l() and ll may be effectively employed.

With this arrangement, so long as the voltage under supervision iswithin a predetermined range, no signal is applied to the detlectingplates, with the luminous area staying motionless at a position on thescreen, and it is only when the voltage under supervision iluctuatesoutside the predetermined range that the deflecting plates are impressedwith a voltage suicient to move the luminous area on the screen to aposition corresponding to the preset position of either of the twophotoelectric means dening the range, so that light 'from the luminousarea illuminates the photoelectric element suiciently for the auxiliaryrelay to be actuated.

In FIGURE 9 there is shown a cathode-ray tube 1 including a deflectingsystem 3 consisting of a pair of spaced plates 31 and 32. Plate 31 isconnected to a deflection control circuit 51 consisting of a Schmittcircuit A, while plate 32 is connected to another deilection controlcircuit 52 consisting of a Schmitt circuit A and a NOT circuit B. Theinput sides of the two Schmitt circuits are connected to a terminal 53,t-o which a voltage to be supervised is applied.

The wiring diagrams of the Schmitt circuit and the NOT circuit are shownby way of example in FIGURES 10 and 11, respectively. As shown in FIGURE10, the Schmitt circuit includes two triodes 54 and 55. With a voltagesupplied from a B+ source, the grid 57 of triode 54 is biased negativedue to a voltage drop across variable resistor 56 so that this triodebecomes non-conducting. With triode 54 cut 0H, no anode current flowstherethrough, causing no voltage drop across resistor 58. This makes thegrid of triode 55 positive with respect to its cathode 60, so that thistriode is kept conducting.

In FIGURE 11, the NOT circuit has a triode 61 whose cathode 62 is biasedpositive so that when a relatively high voltage is applied to grid 63, arelatively low output appears at terminal 64, while when the voltageapplied to the grid is relatively low, the output appearing at theterminal is relatively high.

As previously mentioned, a voltage to be regulated or a voltageproportional thereto is applied to terminal 53 and thence to the inputsides of the two Schmitt circuits. Now suppose that it be intended tokeep the voltage within the range of 60 to 70 v. Appropriate adjustmentof the respective variable resistors 56 of the two Schmitt circuitsmakes it possible that the Schmitt circuit of circuit Sl operates whenthe voltage applied to terminal 53 exceeds 70 v. or a value proportionalthereto, and that the Schmitt circuit of circuit 52 operates when thevoltage applied to terminal 53 exceeds 60 v. or a value proportionalthereto.

So long as the applied voltage is within the range of 60 to 70 v., theSchmitt circuit of circuit 51 does not operate, so that the triode S5 isconducting, applying a voltage V1 to the detlecting plate 31, thisvoltage V1 being equal to the voltage of the B source minus the dropacross resistor 65. On the other hand, the Schmitt circuit of circuit S2is in operation, with its triode 55 non-conducting, so that the triode61 of the NOT circuit is conducting, applying to the dellecting plate 32a voltage V2 which is equal to the voltage of the B source minus thedrop across resistor 66. If the circuits are so arranged that the twovoltages V1 and V2 become equal, the electron beam within thecathode-ray tube experiences no deflection and the luminous areaproduced on the screen of the tube is held at the center thereof.

When the input voltage at terminal S3 happens to rise above 70 v., theSchmitt circuit of circuit 51 operates so that the triode 55 -becomesnon-conducting and the voltage applied to the detlecting plate 31becomes equal t0 the voltage of the B source, This causes a deflectionof the electron beam proportional to the difference between the twovoltages V1 and V2, and a corresponding displacement of the luminousarea on the screen. Then, with a photoelectric means 121 preset to aposition correspending to the displaced position of the luminous area,

light therefrom falls upon the photoelectric element contained in thephotoelectric means sufliciently to produce an output, which isamplified by an amplifier 161 to actuate an auxiliary relay 171. Uponactuation of the relay, an automatic control system operates to reducethe voltage under control to a required level. When the voltage has thusbeen decreased below 70 v., the Schmitt circuit of circuit 51 isrendered inoperative again, so that the voltage V1 is reduced to itsinitial level, i.e., equal to V2, and the luminous area on the screen isreturned to the center thereof; consequently, no light therefrom entersthe photoelectric means 121 and the relay 171 is de-energized.

If the voltage at terminal 53 decreases below 60 v., the triode 54 ofthe Schmitt circuit of circuit 52 becomes non-conducting, rendering thetriode 55 conducting and the triode 61 non-conducting; consequently, thevoltage V2 becomes equal to the voltage of the B source, This voltage isapplied to the deflecting plate 32, whereby the luminous area on thescreen is displaced in the direction opposite to that in the previouscase where the voltage to be regulated exceeded 70 v. A photoelectricmeans 122 is preset to a position corresponding to the displacedposition of the luminous area, so that light therefrom falls -on thephotoelectric element to excite it. The output therefrom is amplified byan amplifier 162 to actuate an auxiliary relay 172. Upon actuation ofthe relay, the automatic control system operates to increase the voltageapplied to terminal 53 until it exceeds 60 v., when the circuit 52recovers its operation and the luminous area on the screen returns tothe center thereof and the control system stops its operation. Y

It will be apparent from the foregoing that with these circuitarrangements, the luminous area on the screen of the cathode-ray tube isbrought to a predetermined position thereon when the voltage undersupervision has gone outside a prescribed range, so ythat howeverrapidly the voltage may iiuctuate outside the range, a sufficient amountof light from the luminous area enters the photoelectric means for theauxiliary relay to be actuated without fail.

.It should be recognized that the embodiments disclosed herein aremerely representative and that further modifications and changes may bemade without departing from the true scope and spirit of the invention.

What is claimed is:

1. An electrical system for generating an output signal upon occurrenceof a predetermined input signal value, comprising a cathode ray tubeincluding means for generating an electron beam, a screen whichluminesces at points of impingement of said beam thereon, and beamdeiiecting means coupled to the system input and operable to deiiectsaid beam to different positions on said screen in response to differentinput signal values; light-sensitive means for receiving light from suchluminescence and positioned adjacent said screen at a locationcorresponding to a predetermined input deflection signal value; adeflection limiter circuit interposed in said system input and coupledto said detiecting means, said limiter circuit including circuit meansoperable to stop beam deiiection at the location of said light-sensitivemeans; and output means responsive to said light sensitive meansincluding means for generating an output signal upon occurrence of aninput signal value causing beam deflection to such location.

2. The system defined in claim 1 further including positioning meanscarrying said light-sensitive means and operable to adjust the positionthereof to different deflection locations along said screen, and whereinsaid detiection limiter circuit includes adjustable circuit meansoperatively coupled to said positioning means whereby positioning of thelatter adjusts maximum beam deection permitted by said limiter circuitto the location of said lightsensitive means.

3. The system defined in claim 1 wherein said deflection limiter circuitincludes additional circuit means operable to preclude deflection ofsaid beam when the input signal is less than a preselected value.

4. The system defined in claim 3 wherein said system includes first andsecond such light-sensitive means at iirst and second locations,respectively, and associated first and second such deflection limitercircuits, the preselected value for said first limiter circuit beinggreater than the preselected value for said second limiter circuit, andNOT circuit means coupled with the output of said second limiter circuitwhereby the latter is rendered operative to deflect said beam to thelocation of the second lightsensitive means when said input signal valueis less than its preselected value and to preclude such deection whensaid input signal value is greater than its preselected value, wherebydeiiection to said first and second locations occurs when said inputsignal value is greater than and less than the range established by thepreselected values for said first and second limiter circuits,respectively.

5. The system defined in claim 1 wherein said cathode ray tube includesa curved front face having said screen on the inside surface thereof,and wherein said system further includes positioning means carrying saidlightsensitive means thereon and operable to adjust the position thereofto different deiiection locations along said screen, said positioningmeans comprising an arm pivotally mounted at substantially the center ofcurvature of said front face and carrying said light-sensitive means atthe outer extremity thereof adjacent said front face.

6. The system defined in claim 1 wherein said beam deecting means isoperable to deiiect said beam to impinge upon said screen at locationslying substantially along a linear path thereon, said system furtherincluding lan elongated optical lens extending along said path andhaving a substantially convex cross section throughout whereby tocollect light from luminescence of said screen and focus the same onsaid light-sensitive means at any location along said path.

7. The system defined in claim 1 wherein said output means comprises arelay and actuating means operable to actuate said relay in response tooccurrence of said input signal value causing detiection to suchlocation.

References Cited by the Examiner FOREIGN PATENTS 453,248 9/36GreatBritain.

DAVID G. REDINBAUGH, Primary Examiner.

1. AN ELECTRICAL SYSTEM FOR GENERATING AN OUTPUT SIGNAL UPON OCCURRENCEOF A PREDETERMINED INPUT SIGNAL VALUE, COMPRISING A CATHODE RAY TUBEINCLUDING MEANS FOR GENERATING AN ELECTRON BEAM, A SCREEN WHICHLUMINESCES AT POINTS OF IMPINGEMENT OF SAID BEAM THEREON, AND BEAMDEFLECTING MEANS COUPLED TO THE SYSTEM INPUT AND OPERABLE TO DEFLECTSAID BEAM TO DIFFERENT POSITIONS ON SAID SCREEN IN RESPONSE TO DIFFERENTINPUT SIGNAL VALUES; LIGHT-SENSITIVE MEANS FOR RECEIVING LIGHT FROM SUCHLUMINESCENCE AND POSITION ADJACENT SAID SCREEN AT A LOCATIONCORRESPONDING TO A PREDETERMINED INPUT DEFLECTION SIGNAL VALUE; ADEFLECTION LIMITER CIRCUIT INTERPOSED IN SAID SYSTEM INPUT AND COUPLEDTO SAID DEFLECTING MEANS, SAID LIMITER CIRCUIT INCLUDING CIRCUIT MEANSOPERABLE TO STOP BEAM DEFLECTION AT THE LOCATION OF SAID LIGHT-SENSITIVEMEANS; AND OUTPUT MEANS RESPONSIVE TO SAID LIGHT SENSITIVE MEANSINCLUDING MEANS FOR GENERATING AN OUTPUT SIGNAL UPON OCCURRENCE OF ANINPUT SIGNAL VALUE CAUSING BEAM DEFLECTION TO SUCH LOCATION.